Preferred auditory temporal processing regimes and auditory-motor synchronization

Auditory and motor priming of metric structure improves understanding of degraded speech

Speech comprehension is enhanced when preceded (or accompanied) by a congruent rhythmic prime reflecting the metrical sentence structure. Although these phenomena have been described for auditory and motor primes separately, their respective and synergistic contribution has not been addressed. In this experiment, participants performed a speech comprehension task on degraded speech signals that were preceded by a rhythmic prime that could be auditory, motor or audiomotor. Both auditory and audiomotor rhythmic primes facilitated speech comprehension speed. While the presence of a purely motor prime (unpaced tapping) did not globally benefit speech comprehension, comprehension accuracy scaled with the regularity of motor tapping. In order to investigate inter-individual variability, participants also performed a Spontaneous Speech Synchronization test. The strength of the estimated perception-production coupling correlated positively with overall speech comprehension scores. These findings are discussed in the framework of the dynamic attending and active sensing theories.

Amplitude envelope onset characteristics modulate phase locking for speech auditory-motor synchronization

The spontaneous speech-to-speech synchronization (SSS) test has been shown to be an effective behavioral method to estimate cortical speech auditory-motor coupling strength through phase-locking value (PLV) between auditory input and motor output. This study further investigated how amplitude envelope onset variations of the auditory speech signal may influence the speech auditory-motor synchronization. Sixty Mandarin-speaking adults listened to a stream of randomly presented syllables at an increasing speed while concurrently whispering in synchrony with the rhythm of the auditory stimuli whose onset consistency was manipulated, consisting of aspirated, unaspirated, and mixed conditions. The participants' PLVs for the three conditions in the SSS test were derived and compared. Results showed that syllable rise time affected the speech auditory-motor synchronization in a bifurcated fashion. Specifically, PLVs were significantly higher in the temporally more consistent conditions (aspirated or unaspirated) than those in the less consistent condition (mixed) for high synchronizers. In contrast, low synchronizers tended to be immune to the onset consistency. Overall, these results validated how syllable onset consistency in the rise time of amplitude envelope may modulate the strength of speech auditory-motor coupling. This study supports the application of the SSS test to examine individual differences in the integration of perception and production systems, which has implications for those with speech and language disorders that have difficulty with processing speech onset characteristics such as rise time.

Auditory-motor synchronization varies among individuals and is critically shaped by acoustic features

The ability to synchronize body movements with quasi-regular auditory stimuli represents a fundamental trait in humans at the core of speech and music. Despite the long trajectory of the study of such ability, little attention has been paid to how acoustic features of the stimuli and individual differences can modulate auditory-motor synchrony. Here, by exploring auditory-motor synchronization abilities across different effectors and types of stimuli, we revealed that this capability is more restricted than previously assumed. While the general population can synchronize to sequences composed of the repetitions of the same acoustic unit, the synchrony in a subgroup of participants is impaired when the unit's identity varies across the sequence. In addition, synchronization in this group can be temporarily restored by being primed by a facilitator stimulus. Auditory-motor integration is stable across effectors, supporting the hypothesis of a central clock mechanism subserving the different articulators but critically shaped by the acoustic features of the stimulus and individual abilities.

Explaining flexible continuous speech comprehension from individual motor rhythms

When speech is too fast, the tracking of the acoustic signal along the auditory pathway deteriorates, leading to suboptimal speech segmentation and decoding of speech information. Thus, speech comprehension is limited by the temporal constraints of the auditory system. Here we ask whether individual differences in auditory-motor coupling strength in part shape these temporal constraints. In two behavioural experiments, we characterize individual differences in the comprehension of naturalistic speech as function of the individual synchronization between the auditory and motor systems and the preferred frequencies of the systems. Obviously, speech comprehension declined at higher speech rates. Importantly, however, both higher auditory-motor synchronization and higher spontaneous speech motor production rates were predictive of better speech-comprehension performance. Furthermore, performance increased with higher working memory capacity (digit span) and higher linguistic, model-based sentence predictability-particularly so at higher speech rates and for individuals with high auditory-motor synchronization. The data provide evidence for a model of speech comprehension in which individual flexibility of not only the motor system but also auditory-motor synchronization may play a modulatory role.

Studying rhythm processing in speech through the lens of auditory-motor synchronization

Continuous speech is organized into a hierarchy of rhythms. Accurate processing of this rhythmic hierarchy through the interactions of auditory and motor systems is fundamental to speech perception and production. In this mini-review, we aim to evaluate the implementation of behavioral auditory-motor synchronization paradigms when studying rhythm processing in speech. First, we present an overview of the classic finger-tapping paradigm and its application in revealing differences in auditory-motor synchronization between the typical and clinical populations. Next, we highlight key findings on rhythm hierarchy processing in speech and non-speech stimuli from finger-tapping studies. Following this, we discuss the potential caveats of the finger-tapping paradigm and propose the speech-speech synchronization (SSS) task as a promising tool for future studies. Overall, we seek to raise interest in developing new methods to shed light on the neural mechanisms of speech processing.

Speech-to-Speech Synchronization protocol to classify human participants as high or low auditory-motor synchronizers

The ability to synchronize a motor action to a rhythmic auditory stimulus is often considered an innate human skill. However, some individuals lack the ability to synchronize speech to a perceived syllabic rate. Here, we describe a simple and fast protocol to classify a single native English speaker as being or not being a speech synchronizer. This protocol consists of four parts: the pretest instructions and volume adjustment, the training procedure, the execution of the main task, and data analysis. For complete details on the use and execution of this protocol, please refer to Assaneo et al. (2019a).

The Relationship Between Auditory-Motor Integration, Interoceptive Awareness, and Self-Reported Stuttering Severity

Stuttering is a neurodevelopmental speech disorder associated with motor timing that differs from non-stutterers. While neurodevelopmental disorders impacted by timing are associated with compromised auditory-motor integration and interoception, the interplay between those abilities and stuttering remains unexplored. Here, we studied the relationships between speech auditory-motor synchronization (a proxy for auditory-motor integration), interoceptive awareness, and self-reported stuttering severity using remotely delivered assessments. Results indicate that in general, stutterers and non-stutterers exhibit similar auditory-motor integration and interoceptive abilities. However, while speech auditory-motor synchrony (i.e., integration) and interoceptive awareness were not related, speech synchrony was inversely related to the speaker’s perception of stuttering severity as perceived by others, and interoceptive awareness was inversely related to self-reported stuttering impact. These findings support claims that stuttering is a heterogeneous, multi-faceted disorder such that uncorrelated auditory-motor integration and interoception measurements predicted different aspects of stuttering, suggesting two unrelated sources of timing differences associated with the disorder.

Musical Sophistication and Speech Auditory-Motor Coupling: Easy Tests for Quick Answers

Musical training enhances auditory-motor cortex coupling, which in turn facilitates music and speech perception. How tightly the temporal processing of music and speech are intertwined is a topic of current research. We investigated the relationship between musical sophistication (Goldsmiths Musical Sophistication index, Gold-MSI) and spontaneous speech-to-speech synchronization behavior as an indirect measure of speech auditory-motor cortex coupling strength. In a group of participants (n = 196), we tested whether the outcome of the spontaneous speech-to-speech synchronization test (SSS-test) can be inferred from self-reported musical sophistication. Participants were classified as high (HIGHs) or low (LOWs) synchronizers according to the SSS-test. HIGHs scored higher than LOWs on all Gold-MSI subscales (General Score, Active Engagement, Musical Perception, Musical Training, Singing Skills), but the Emotional Attachment scale. More specifically, compared to a previously reported German-speaking sample, HIGHs overall scored higher and LOWs lower. Compared to an estimated distribution of the English-speaking general population, our sample overall scored lower, with the scores of LOWs significantly differing from the normal distribution, with scores in the ∼30th percentile. While HIGHs more often reported musical training compared to LOWs, the distribution of training instruments did not vary across groups. Importantly, even after the highly correlated subscores of the Gold-MSI were decorrelated, particularly the subscales Musical Perception and Musical Training allowed to infer the speech-to-speech synchronization behavior. The differential effects of musical perception and training were observed, with training predicting audio-motor synchronization in both groups, but perception only in the HIGHs. Our findings suggest that speech auditory-motor cortex coupling strength can be inferred from training and perceptual aspects of musical sophistication, suggesting shared mechanisms involved in speech and music perception.